We wish to analyze the stuctural basis for T cell corecognition of antigen and major histocompatibility complex (MHC) proteins, using purified, soluble forms of the T cell receptor. We will also make antibodies against particular V alpha and V beta domains of soluble T cell receptor proteins to examine possible regulation of V region expression during T cell ontogeny and during the immune response. We will produce soluble T cell receptor protein from chimeric genes containing T cell receptor V region exons and immunoglobulin constant region exons expressed in B cells under the control of immunoglobulin regulatory elements. Chimeric antibodies with T cell receptor binding sites will be purified and used in experiments to determine the specificity and binding constants (association, dissociation and equilibrium) for the T cell receptor to its ligands; peptide antigen and MHC, both individually and together. Comparison of affinities for different antigens and MHC proteins with data on the activation of the original T cell will be used to understand the role of T cell receptor affinity in T cell activation and to determine the relative contribution of antigen and MHC in normal MHC- restricted recognition of antigen. These chimeric proteins will be crystallized for x-ray diffraction determination of their crystal structure. Proteins containing individual alpha or beta chain V domains will be used to produce monoclonal antibodies reactive with these particular V regions, since such reagents have been difficult to produce with conventional immunization. These reagents will be used to examine whether there is a developmental progression in the expression of T cell receptor V regions as occurs with immunoglobulin V regions. Since many of the T cell responses to small antigenic determinants seem to utilize a very limited set of T cell receptor V regions, antibodies against suitable V regions will be used to analyze the T cell repertoire during an immune response and to modify it. Such anti-T cell receptor V region reagents may be useful in diagnosis or treatment of certain diseases.